This transcript is from an in-depth dermatopathology teaching session focused on the diagnosis of various vascular lesions. An expert pathologist guides residents and fellows through a series of digital slide cases, covering a wide spectrum of benign, intermediate, and malignant entities.
Key benign diagnoses discussed include Targetoid Hemosiderotic Hemangioma (Hobnail Hemangioma), Glomus Tumor, Tufted Angioma, Pyogenic Granuloma, Angiokeratoma, Lymphangioma, and various hemangioma subtypes, highlighting their characteristic morphologies like hobnail cells, "cannonball" tufts, and lobularity. The session also covers reactive processes such as Intravascular Papillary Endothelial Hyperplasia (Masson's Tumor) and Stasis Dermatitis. Malignant lesions, particularly Angiosarcoma and Kaposi Sarcoma, are examined in detail, with an emphasis on distinguishing their infiltrative growth patterns and cytologic atypia from benign mimics. Throughout the session, the importance of clinical context—such as patient age, lesion location, and history of radiation—is repeatedly stressed as crucial for accurate diagnosis. Differential diagnoses are thoroughly explored for each case, providing a comprehensive and practical guide to vascular pathology.
A Comprehensive Guide to Vascular Lesions in Dermatopathology
0:00:25 Targetoid Hemosiderotic Hemangioma (Hobnail Hemangioma): This benign lesion is characterized by superficial, dilated "cavernous" channels with hobnail endothelial cells, sitting above deeper, compressed, slit-like channels that "trickle" between collagen. Differential diagnoses include angiokeratoma (which is entrapped by the epidermis) and Kaposi sarcoma. On breast skin post-radiation, a similar pattern is called an atypical vascular lesion.
0:08:03 Glomus Tumor: This benign tumor presents as nodules of monotonous, small, round, dark cells clustered around vessels deep in the dermis. It's a pericytic tumor, and its appearance can mimic sweat gland tumors like spiradenoma. The cells are typically arranged in multilayered, concentric "onion skinning" patterns around vessels.
0:12:46 Tufted Angioma / Kaposiform Hemangioendothelioma: These are on a spectrum, characterized by multifocal, "cannonball-like" nodules of compressed, slit-like vascular channels infiltrating the dermis and subcutis. They are often set within a background of dilated, irregular lymphatic channels. In large lesions in infants, they can cause Kasabach-Merritt syndrome (platelet trapping).
0:18:13 Angiosarcoma: A malignant tumor showing a busy, cellular dermis with infiltrative growth. It forms anastomosing vascular channels that dissect between collagen bundles. Key features include significant endothelial cell atypia, hobnailing, and hypercellularity. The clinical context is critical; it's often seen in sun-damaged skin of the elderly head and neck or in previously radiated sites.
0:24:21 Angiomyoma: A benign, circumscribed nodule composed of smooth muscle and multiple vascular lumens of varying sizes. Unlike other leiomyomas, the muscle swirls around each vessel rather than forming distinct fascicles. It is classically a painful nodule on the lower leg of an adult woman.
0:28:10 Kaposi Sarcoma (Nodular Stage): This stage presents as a distinct nodule, often with an epidermal collarette. Microscopically, it features fascicles of plump spindle cells with slit-like spaces containing extravasated red blood cells. A key diagnostic clue is the "sieve-like" pattern seen when fascicles are cut in cross-section. An HHV-8 immunostain is highly specific for diagnosis.
0:36:58 Glomeruloid Hemangioma: Characterized by tufts of capillaries protruding into dilated vascular spaces in a crescentic or "glomeruloid" pattern. This finding is strongly associated with POEMS syndrome.
0:38:50 Erythema Elevatum Diutinum (EED): A rare form of fibrosing vasculitis. It shows leukocytoclastic vasculitis (neutrophils, fibrin, nuclear dust in vessel walls) with a prominent "onion-skin" concentric fibrosis around the affected vessels.
0:43:36 Pyogenic Granuloma (Lobular Capillary Hemangioma): A benign, reactive proliferation that forms a polypoid, often ulcerated papule with an epidermal collarette. It is composed of lobules of packed capillaries in an edematous stroma. It can have plump endothelial cells and mitoses, but lacks significant atypia.
0:46:28 Intravascular Papillary Endothelial Hyperplasia (IPEH / Masson's Tumor): A reactive process of an organizing thrombus within a pre-existing vessel. It features complex papillary structures composed of fibrin cores lined by bland endothelial cells. Finding the connection to a solid thrombus is key to distinguishing it from angiosarcoma.
0:52:10 Angiokeratoma: This lesion features dilated, cavernous vascular channels that are entrapped high in the papillary dermis, with the epidermis wrapping down and around them. This is distinct from a hobnail hemangioma, where the vessels are below the epidermis.
0:56:12 Angiolymphoid Hyperplasia with Eosinophilia (ALHE) / Epithelioid Hemangioma: Composed of lobules of vessels lined by plump, epithelioid endothelial cells with abundant cytoplasm and hobnailing. The background stroma contains a prominent inflammatory infiltrate of lymphocytes and eosinophils.
1:04:14 Hidradenoma: A benign sweat gland tumor that can mimic a glomus tumor due to its nodular growth and monotonous cells. Key distinguishing features are the presence of true ducts, clear cell change, and connection to the epidermis. It will be positive for keratins, unlike a glomus tumor.
1:11:15 Stasis Dermatitis: A common reactive change on the lower legs of adults. It shows clusters of thick-walled capillaries and venules in the superficial dermis, often with fibrosis and hemosiderin deposition. When severe, it can mimic Kaposi sarcoma (pseudo-Kaposi).
1:14:40 Hibernoma: A benign tumor of brown fat. It is composed of a mixture of three cell types: mature white fat, multivacuolated bubbly cells (resembling lipoblasts but with small nuclei), and large cells with granular, eosinophilic cytoplasm packed with mitochondria.
1:21:44 Angiosarcoma (Post-Radiation): This case shows a highly cellular, atypical angiosarcoma arising in a background of severe radiation-associated changes, including dense dermal sclerosis, hemorrhage, and dilated lymphatic channels (lymphedema). Post-radiation angiosarcomas are often associated with c-MYC amplification.
1:31:32 Aneurysmal Dermatofibroma: A variant of dermatofibroma characterized by large, blood-filled, "aneurysmal" spaces within the typical spindle cell proliferation. The presence of hemorrhage and blood-filled spaces can cause it to mimic a primary vascular tumor.
1:36:50 Kaposi Sarcoma (Patch Stage): The earliest stage can be subtle. It shows an increased number of irregular, jagged vascular channels in the upper dermis that appear to dissect between collagen bundles. There are often associated spindle cells, extravasated red blood cells, hemosiderin, and plasma cells.
1:45:50 Lymphangioma (Lymphatic Malformation): Characterized by dilated, cavernous, thin-walled channels in the dermis, typically filled with pale pink lymph fluid rather than blood. The endothelial lining is flat and bland. It can have overlapping features with angiokeratoma if the channels are high in the dermis.
1:59:21 Spindle Cell Hemangioma: A benign lesion, often in the subcutis, featuring a biphasic pattern of cavernous vascular spaces mixed with solid nodules of bland spindle cells and epithelioid endothelial cells. Though benign, they can be multifocal. They are associated with Maffucci syndrome.
2:08:00 Superficial Angiomyxoma (Cutaneous Myxoma): A benign, multilobular, hypocellular lesion with a prominent myxoid (blue, mucinous) stroma. It contains bland spindle cells and branching, thin-walled blood vessels. Scattered neutrophils are a helpful diagnostic clue.
2:19:21 Venous Lake: A common lesion in sun-damaged skin, representing a large, dilated, thin-walled venous channel in the superficial dermis. On biopsy, the blood often washes out, leaving a large, empty space lined by flat endothelium.
2:22:12 Infantile Hemangioma: A common tumor of infancy that is highly cellular in its proliferative phase. It forms dense, back-to-back lobules of capillaries lined by plump endothelial cells. A key diagnostic feature is positivity for the GLUT1 immunostain.
2:27:45 Temporal Arteritis (Giant Cell Arteritis): A large vessel vasculitis showing a dense inflammatory infiltrate of lymphocytes, histiocytes, and multinucleated giant cells destroying the wall of a muscular artery. The inflammation is often centered on a disrupted internal elastic lamina.
2:31:57 Microvenular Hemangioma: A rare, benign vascular proliferation of small, irregular venules that trickle and infiltrate between dermal collagen bundles. Its infiltrative pattern can mimic Kaposi sarcoma or angiosarcoma, but it lacks atypia.